Advanced oxidation processes are a type of new techniques that have been widely adopted in treatment of wastewater containing high-concentrated toxic pollutants since 1980s. In most of advanced oxidation processes, highly reactive hydroxyl radicals (.OH) are generated and can mineralize or effectively degrade most of organic pollutants, and even completely converse them into harmless, small inorganic molecules. In terms of different oxidants and catalytic conditions adopted in the reaction, advanced oxidation processes are generally grouped into 6 categories: chemical oxidation process, chemical catalytic oxidation process, wet oxidation process, supercritical water oxidation process, photochemical or photochemical catalytic oxidation process, and electrochemical oxidation-reduction process. Among these processes, the photochemical oxidation process has become a research focus worldwide due to its mild reaction conditions, high oxidation activity and wide applicability in degrading recalcitrant pollutants. Currently, heterogeneous photocatalytic oxidation and homogeneous photo-oxidation are two types of most-studied photochemical oxidation processes. The most popular method to realize heterogeneous photocatalytic oxidation is to adopt semiconductive materials, and this method can degrade nearly all organics in the water. However, the homogeneous photo-oxidation, realized by coupling with ozone (O3), hydrogen peroxide (H2O2) and Fenton reagent, presents much higher oxidation capacity and photolytic rate than heterogeneous photocatalysis. Therefore, it has been regarded as a simple and effective method in treatment of wastewater, and has attracted increasing attention from those who involves in environmental protection. Many related research findings have been published all over the world (U.S. Pat. No. 4,012,321, U.S. Pat. No. 6,555,835, WO patent 93/08129, China Patent 2009120021).
Dyeing wastewater is characterized with high chemical oxygen demand (COD), high chromaticity, strong acidity or alkalinity due to a large amount of organic substances and salts it contains. As a result, it poses a constant challenge in the field of wastewater treatment. The common homogeneous photo-oxidation processes, such as those adopting ultraviolet/O3, ultraviolet/H2O2 and ultraviolet/Fenton systems, are somewhat effective in treatment of dyeing wastewater. However, these systems are constrained by many factors and are not practically feasible. For example, O3 needs to be in situ generated, which consequently increases construction cost and operating expenses. In addition, the gas-liquid mass transfer existing therein lowers down operating efficiency as well. When Fenton reaction is adopted, a large amount of sludge containing metallic oxides will be generated, which not only leads to secondary pollution but also makes it hard to realize complete decolorization of water. The UV/H2O2 method is simpler in operation and maintenance in comparison with the above mentioned two methods, but its performance is severely affected by substances coexisting in wastewater. Besides, this method is also characterized with poor selectivity, large reagent consumption and high operating cost.
Acetylacetone is a small molecular diketone famously existing in two tautomeric forms (i.e. keto and enol forms) that rapidly interconvert. It is widely used as catalyst or cocatalyst, such as accelerant for oxygen oxidation, catalyst for pyrolysis or hydrogenation of petroleum, catalyst for isomerization process, and catalyst for polymerization of lower alkenes. The enol form of acetylacetone presents a large absorption cross-section in the ultraviolet region, and its gaseous phase can generate hydroxyl radicals (·OH) under ultraviolet irradiation. However, the photochemical properties of liquid-phase acetylactone have never been reported yet.